When performing electroencephalograms, in order to ensure repeatability and allow comparison of patient data to norms, it is desirable to place EEG scalp electrodes according to the internationally standardized “10-20” pattern; the pattern allows for up to sixty-five electrodes for receiving signals from both cerebral hemispheres.
Some technicians measure electrode placements according to the 10-20 pattern, and attach electrodes individually with a collodion adhesive. Each electrode typically also has a contact surface moistened with an electrically conductive paste. While effective, this technique is very time consuming, especially where many electrodes are required; this technique is failure prone in that individual electrodes may fall off or need adjustment to perform correctly.
A prior technique for positioning scalp electrodes is to fabricate an elastomeric cap and attach electrodes to the cap. Typically, each electrode is on an interior surface of the cap and connects through a hole to a lead exterior to the cap. The leads are then gathered into a cable and connected to an electroencephalograph. The electroencephalograph can provide information regarding electrical activity in the brain.
An optode is a device for transmitting or receiving light into or through tissue. An optode is a device for coupling light between an optical fiber and tissue, such as skin, as described in our previous patent applications 61/048,446 filed Apr. 28, 2008, and PCT/US09/41560 filed Apr. 23, 2009, the disclosure of which is incorporated herein by reference.
Recent research has demonstrated that useful information can be obtained by passing infrared light into the skull from one or more transmit optodes, and receiving that light at one or more receive optodes. In some systems, individual optodes may serve alternately as transmit and receive optodes. Typically, the light is at two or more wavelengths, and information regarding patterns of brain oxygenation is obtained by measuring differences in attenuation at the two or more wavelengths along paths between optodes. Brain oxygenation patterns have been shown to correlate with patterns of neurological activity in the brain; these patterns are therefore useful for functional neuroimaging.
In order to obtain repeatable, useful, indications of patterns of brain oxygenation, it is desirable that optodes be held in a preferred orientation and contact with the scalp. Further, if simultaneous electroencephalography is desired, it is desirable that electrodes also be held firmly in evenly spaced positions conforming to a 10/20 pattern or to an extrapolated 10/20 pattern. It has been found that a simple elastomeric cap fails to hold optodes and electrodes in proper positions and orientations relative to a subject's head and scalp for optimum results, particularly when the subject is physically active.